Method and apparatus to reduce arcing in electrodeless lamps

Abstract

A lamp and methods of forming are shown. In one example, a dielectric layer is formed over a gap between conductors in a plasma lamp. Electric arcing is reduced or eliminated, thus allowing tighter gaps and/or higher voltages. In one example a glass frit method is used to apply the dielectric layer. A lamp is shown with a barrier layer that prevents tarnish such as tarnish from sulfur exposure. The barrier layer reduces or prevents degradation of the lamp due to conversion of a conductor material to non-conductive tarnish material.

1. A electrodeless plasma lamp comprising:
 a lamp body comprising a dielectric material, the lamp body having an electrically conductive coating on an outer surface of the lamp body; 
 an radio RF power source configured to provide RF power to the lamp body; 
 a bulb adjacent to the lamp body, the bulb containing a fill that forms a plasma when the RF power is coupled to the fill from the lamp body; and 
 a dielectric coating over at least a portion of the conductive coating, the dielectric coating having a higher breakdown voltage than air and covering a gap in the conductive coating in a region adjacent to the bulb. 
 
     
     
       2. The electrodeless plasma lamp of  claim 1 , wherein the dielectric coating includes a breakdown voltage greater than or equal to 40 V/μm. 
     
     
       3. The electrodeless plasma lamp of  claim 1 , wherein the dielectric coating is in direct contact with at least a portion of the conductive coating. 
     
     
       4. The electrodeless plasma lamp of  claim 1 , wherein the dielectric coating maintains its material properties at temperatures up to 350 degrees Celsius. 
     
     
       5. The electrodeless plasma lamp of  claim 1 , wherein the dielectric coating is substantially transparent. 
     
     
       6. The electrodeless plasma lamp of  claim 1 , wherein the dielectric coating includes a coefficient of thermal expansion that substantially matches the coefficient of thermal expansion of the lamp body. 
     
     
       7. The electrodeless plasma lamp of  claim 1 , wherein the dielectric coating includes a glass frit coating. 
     
     
       8. The electrodeless plasma lamp of  claim 7 , wherein the glass frit coating is a silicon dioxide glass frit coating. 
     
     
       9. The electrodeless plasma lamp of  claim 1 , wherein the conductive coating includes a noble metal conductor. 
     
     
       10. The electrodeless plasma lamp of  claim 1 , further including a barrier layer coupled over at least a portion of the conductive coating. 
     
     
       11. The electrodeless plasma lamp of  claim 10 , wherein the barrier layer is formed from a conductive material. 
     
     
       12. The electrodeless plasma lamp of  claim 10 , wherein the barrier is formed from a material that prevents sulfur attack on the conductive coating. 
     
     
       13. The electrodeless plasma lamp of  claim 12 , wherein the barrier layer includes nickel. 
     
     
       14. The electrodeless plasma lamp of  claim 1 , wherein frequency of the RF power source is adjusted in response to changing conditions of the fill during startup. 
     
     
       15. The electrodeless plasma lamp of  claim 1 , wherein the lamp body forms a lamp chamber and the bulb is positioned at least partially within the lamp chamber. 
     
     
       16. The electrodeless plasma lamp of  claim 1 , wherein the conductive coating has a thickness less than about 20 microns. 
     
     
       17. The electrodeless plasma lamp of  claim 1 , wherein the conductive coating comprises molybdenum. 
     
     
       18. The electrodeless plasma lamp of  claim 1 , wherein a shortest distance between an end of the bulb and a point on a RF feed traverses at least one electrically conductive material of the lamp body. 
     
     
       19. The electrodeless plasma lamp of  claim 18 , wherein the bulb has an exposed end from which light exits the plasma lamp, and a concealed end, the shortest distance being between the concealed end of the bulb and the RF feed. 
     
     
       20. The electrodeless plasma lamp of  claim 19 , wherein the at least one electrically conductive material is electrically coupled to the electrically conductive coating of the lamp body. 
     
     
       21. A method comprising:
 forming a conductive coating over at least a portion of a lamp body comprising a dielectric material; 
 placing a bulb into an opening within the lamp body, the bulb containing a fill that forms a plasma when RF power is coupled to the fill from the lamp body; and 
 forming a dielectric coating over at least a portion of the conductive coating, the dielectric coating having a higher breakdown voltage than air and being formed over a gap between two portions of the conductive coating adjacent to the bulb. 
 
     
     
       22. The method of  claim 21 , wherein forming the dielectric coating comprises:
 coating at least a portion of the conductive coating with a glass frit slurry; and 
 heating the glass frit slurry to remove a carrier material and adhere the glass frit to a surface of the conductive coating. 
 
     
     
       23. The method of  claim 22 , wherein coating at least a portion of the conductive coating with a glass frit slurry includes coating over a portion of the conductive coating. 
     
     
       24. The method of  claim 22 , wherein coating at least a portion of the conductive coating with the glass frit slurry includes dipping at least a portion of the conductive coating in a glass frit slurry. 
     
     
       25. The electrodeless plasma lamp of  claim 1 , wherein the dielectric coating is to at least reduce arcing in the lamp.